Revolutionary new WTG blade: it's a fabrication

Staff report

On 28 November, the US Energy Department announced 66 research projects selected by its Advanced Research Projects Agency-Energy (ARPA-E) to receive among them a total of $130 million in funding through its 'OPEN 2012' programme. ARPA-E seeks out transformational technologies that show fundamental technical promise but are not ready for private-sector investment. The selected projects encompass 11 technology areas including advanced fuels, advanced vehicle design and materials, building efficiency, grid modernisation, energy storage - and renewable power.
Among the latter is a proposal from GE, Virginia Tech and the National Renewable Energy Laboratory to develop a completely new type of blade for wind turbines that would be entirely familiar to anyone who'd seen the designs for wings of early biplanes - namely a blade stucture based on a light rigid frame with a suitable fabric cover stretched over it. Such fabric-based blades could be manufactured in sections and assembled on-site, enabling the construction of much larger wind turbines with higher efficiency and lower cost, and to help achieve that ambition the three organisations have received a development grant from DoE of a little over $3.7m. The balance of $2m for the 3 year project will come from GE, which is already about a year into the project at its Schenectady facility.
The fabric of the future
This new manufacturing approach is estimated to be able to reduce blade production costs by up to 40%, with the ultimate aim of putting wind energy on an equal economic footing with traditional fossil fuels without government subsidies. It would also pave the way to the construction of longer blades exceeding 130 m. The new blade architecture will be built to achieve a 20 year life with no regular maintenance required to tension the fabric.
This project could fundamentally change the way wind blades are designed, manufactured and installed. With most of the cost of electricity for wind tied up in the initial capital investments made in the wind turbines themselves, new technology advances that reduce these costs could substantially lower the overall cost of wind energy, and GE sees opportunities for cost reduction using this kind of design in materials costs, in manufacturing methods and tools, in transportation and in on-site construction.
This kind of advance will help spur the development of larger, lighter turbines that can capture more wind at lower wind speeds. Current technology doesn't easily allow for construction of turbines that have rotor diameters exceeding 120 metres because of design, manufacturing, assembly, and transportation constraints. Wider, longer wind blades are more difficult to move and manoeuvre, and moulds which form the clamshell fibreglass structure cost millions of dollars to acquire. A fabric-based technology would substantially lower these barriers.
And the ability to build and assemble on site would eliminate many manufacturing and transportation limitations. Altogether, these improvements should help reduce start-up costs and the overall cost of wind power.
'GE is weaving an advanced wind blade that could be the fabric of our clean energy future,' says Wendy Lin, a GE principal engineer and leader on the ARPA-E project. 'The fabric we're developing will be tough, flexible, and easier to assemble and maintain. It represents a clear path to making wind even more cost competitive with fossil fuels.'
Development
GE's research will focus on the use of architectural fabrics, which would be stretched around a metal spaceframe resembling a fishbone. Fabric would be tensioned around ribs that run the length of the blade and specially designed to meet the demands of wind blade operations. Conventional wind blades are constructed from fibreglass, which is heavier and more labour and time-intensive to manufacture.
R&D to date suggests that the fabric decided on will be a species of rubber-flax composite, but these are still early days and the feasibility of the construction method has not yet been demonstrated in terms of WTG performance. The development route therefore is going to be linear, one step at a time. The next stage is to arrive at a conceptual design that can be tested on a 10-20 metre scale, followed by scaled up designs at the National Renewable Engineering Laboratory. The research team is currently looking at joint design (there are many more joints in this kind of structure), blade profile, selection and capability tests on materials, and the selection of a tough and reliable fabric.
National goals
It is estimated that to achieve the national goal of 20% wind power in the U.S., wind blades would need to grow by 50% - a figure that would be virtually impossible to realise given the size constraints imposed by current technology. Lighter fabric blades could make this goal attainable.
"Developing larger wind blades is the key to expanding wind energy into areas we wouldn't think of today as suitable for harvesting wind power. Tapping into moderate wind speed markets, in places like the Midwest, will only help grow the industry in the years to come," comments Wendy Lin.

Caption: cgi showing the new blade structure